diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 7ed72abe59..6a66214a58 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -1776,6 +1776,7 @@ GetBulkInsertState(void)
 	bistate->current_buf = InvalidBuffer;
 	bistate->next_free = InvalidBlockNumber;
 	bistate->last_free = InvalidBlockNumber;
+	bistate->already_extended_by = 0;
 	return bistate;
 }
 
diff --git a/src/backend/access/heap/hio.c b/src/backend/access/heap/hio.c
index c275b08494..21f808fecb 100644
--- a/src/backend/access/heap/hio.c
+++ b/src/backend/access/heap/hio.c
@@ -283,6 +283,24 @@ RelationAddBlocks(Relation relation, BulkInsertState bistate,
 		 */
 		extend_by_pages += extend_by_pages * waitcount;
 
+		/* ---
+		 * If we previously extended using the same bistate, it's very likely
+		 * we'll extend some more. Try to extend by as many pages as
+		 * before. This can be important for performance for several reasons,
+		 * including:
+		 *
+		 * - It prevents mdzeroextend() switching between extending the
+		 *   relation in different ways, which is inefficient for some
+		 *   filesystems.
+		 *
+		 * - Contention is often intermittent. Even if we currently don't see
+		 *   other waiters (see above), extending by larger amounts can
+		 *   prevent future contention.
+		 * ---
+		 */
+		if (bistate)
+			extend_by_pages = Max(extend_by_pages, bistate->already_extended_by);
+
 		/*
 		 * Can't extend by more than MAX_BUFFERS_TO_EXTEND_BY, we need to pin
 		 * them all concurrently.
@@ -409,6 +427,7 @@ RelationAddBlocks(Relation relation, BulkInsertState bistate,
 		/* maintain bistate->current_buf */
 		IncrBufferRefCount(buffer);
 		bistate->current_buf = buffer;
+		bistate->already_extended_by += extend_by_pages;
 	}
 
 	return buffer;
diff --git a/src/include/access/hio.h b/src/include/access/hio.h
index 228433ee4a..9bc563b762 100644
--- a/src/include/access/hio.h
+++ b/src/include/access/hio.h
@@ -32,15 +32,22 @@ typedef struct BulkInsertStateData
 	Buffer		current_buf;	/* current insertion target page */
 
 	/*
-	 * State for bulk extensions. Further pages that were unused at the time
-	 * of the extension. They might be in use by the time we use them though,
-	 * so rechecks are needed.
+	 * State for bulk extensions.
+	 *
+	 * last_free..next_free are further pages that were unused at the time of
+	 * the last extension. They might be in use by the time we use them
+	 * though, so rechecks are needed.
 	 *
 	 * XXX: Eventually these should probably live in RelationData instead,
 	 * alongside targetblock.
+	 *
+	 * already_extended_by is the number of pages that this bulk inserted
+	 * extended by. If we already extended by a significant number of pages,
+	 * we can be more aggressive about extending going forward.
 	 */
 	BlockNumber next_free;
 	BlockNumber last_free;
+	uint32		already_extended_by;
 } BulkInsertStateData;